Worldwide concern over the growing shortages of crude oil supplies has promoted the use of many materials as blending agents in gasoline to extend the fuel supply. Environmental concern has also promoted use of oxygenated gasoline in order to reduce emissions. Methanol, ethanol and t-butanol have emerged as the most widely used alcohol blending agents. Methanol, often in mixes with cosolvents such as tert-butanol, has been used in commercial gasoline.
The use of a polar oxygenates such as methanol, ethanol, butanol, in gasoline blends, however, has far reaching consequences. One of these is the creation of corrosion problems both in the logistic chain and in the vehicle itself. In pipelines and storage tanks, rust which normally would remain on the walls, is loosened by the alcohol and transported through the system.
Of perhaps greater concern with the use of commercial ethanol in gasoline blends are phase separation problems which occur because water containing ethanol has limited solubility in gasoline. When phase separation occurs, corrosion of many of the metals and alloys which make up the vehicle fuel distribution system and the vehicle engine is promoted due to water contacting the metals and metal alloys. Specifically, fuel tank terne plate, (steel coated with an alloy of lead 80-90% and tin 10-20%), zinc and aluminum diecast carburetor and fuel pump parts, brass fittings, steel lines, etc. can corrode when exposed to gasoline-ethanol fuel mixtures.
In addition to bioethanol and t-butyl ethyl ether, biologically-derived butanol or biobutanol is increasingly looked upon as bioethanol substitute because of its advantages over bioethanol from fuel preparation point of view i.e. higher energy content, lower miscibility with water, lower vapour pressure and lower corrosivity. Biobutanol concentration in fuel can reach up to 30% v/v without the need for engine modification. Since the butanol fuel contains oxygen atoms, the stoicliometric air/fuel ratio is smaller than for gasoline and more fuel needs to be injected for the same amount of air induced. The oxygen content has been found to improve combustion, therefore lower CO and HC emissions can be expected. Biobutanol and its mixtures can be used directly in the current gasoline supply system, such as transportation tanks and re-fuelling infrastructure. Biobutanol can be blended with gasoline without additional large-scale supply infrastructure, which is a big benefit as opposed to the bioethanol use. Finally biobutanol is non-poisonous and non-corrosive and it is easily biodegradable and does not cause risk of soil and water pollution.
Compared to ethanol, biobutanol exhibits important advantages upon blending with gasoline. The mixtures have better phase stability in presence of water, low-temperature properties, oxidation stability during long-term storage, distillation characteristics and volatility with respect to possible air pollution. Due to the fact that oxygen content in biobutanol is lower than in ethanol, biobutanol can be added to the gasoline in higher concentrations with respect to regulated limits for the oxygen content in gasoline. Higher biobutanol content in gasoline does not require engine modification. The heating value (energy density) of biobutanol is close to that of gasoline, which has a positive effect on the fuel consumption. Biobutanol has a slightly higher density compared to gasoline but the increase in density of biobutanol/gasoline mixtures is so small that it does not cause problems with fulfilling limits for automotive gasoline containing up to 30% v/v biobutanol.
This problem of corrosion of oxygenate containing gasoline can be remedied to some extent by the use of anhydrous or substantially anhydrous oxygenates as a blending agent. However, if the fuel mixture is exposed to water, oxygenates such as ethanol will experience phase separation. Even in the absence of phase separation, corrosion can be brought about by the presence of trace amounts of acetic acid, acetaldehyde, ethyl acetate and butanol in the fuel blends which are formed during production of the ethanol. Other corrosion problems can arise from dissolved mineral salts, such as highly corrosive sodium chloride, which may be picked up by the fuel during production, storage and transportation.
In the late 1980s, additive companies introduced special corrosion inhibiting additives for oxygenated gasolines. These additives typically are combinations of carboxylic acid type corrosion inhibitors used in conventional unoxygenated gasoline and an amine neutralizer. Many of these materials are assumed to function by becoming adsorbed onto the metallic surface for which protection is desired. This adsorption results in the formation of a physical barrier which interferes with the transfer of corrosive reactants through the metal-solution interface. These additives have been employed with good success in oxygenated gasoline containing ethanol or methanol plus cosolvents. However, what has not been well established is the long term effectiveness of corrosion inhibitors in oxygenated gasolines.
Testing of steel corrosion inhibitors for gasoline is commonly done with the NACE test. (National Association of Corrosion Engineers Method TM-01-72). However, because of OEM concerns about the stability of oxygenated gasoline blends, including continued effectiveness of corrosion inhibitors, additive suppliers have reported heat-aged performance in the NACE test and the Renewal Fuels Association (RFA) has provided an industry guideline that recommends NACE testing after an extended ambient aging period.
Thus, there is presently a need for a corrosion inhibitor that will either curb or prevent the corrosion of conventional systems which are used to store and transport commercial ethanol in gasoline fuel blends and one that will curb or prevent corrosion of the vehicle fuel systems in which these fuels are ultimately used. It is important that the corrosion inhibitor be effective in very small quantities to avoid any adverse effects, such as adding to the gum component of the fuel, etc., as well as to minimize cost. The corrosion inhibitor should also not emulsify water.
Of particular concern is OEM requirements for corrosion inhibitor effectiveness over at least 120 days to emulate expected shelf life. After new automobiles, trucks and motor vehicles, in general, are assembled, their fuel tanks are generally filled to some extent with an appropriate fuel before the vehicles are shipped to their point of sale and delivery to the ultimate customer. Because of the global nature of the motor vehicle industry, with the assembly of the vehicles often times taking place in a different part of the world relative to the point of sale of the vehicle, the fuel that is placed in these fuel tanks often stands unused for extended periods of time during shipment and storage of the vehicles.
During these periods of time, the fuel in the fuel tanks, now effectively being in storage, must retain its initial integrity and not degrade with the degradation exhibiting itself through subsequent starting and running problems in the new vehicle and also by the formation of undesirable deposits in the fuel systems of the vehicles leading to longer term operability problems. The fuel so used must resist gum and sediment formation, minimize oxidation and prevent corrosion in the metallic portions of the fuel system as well as passivate fresh metal surfaces. Likewise, the fuel storage facilities, for example, tankage, pumps and plumbing, at the motor vehicle assembly site are also susceptible to the deposition of these unwanted solid materials from the quantities of stored motor fuels awaiting transfer to the newly assembled vehicles.
The desired storage stability of the fuel is usually attained through the addition of appropriate additives to the fresh fuel. Typically, complex combinations of antioxidants, such as aromatic diamines or hindered phenols, carboxylic acid-based corrosion inhibitors, and metallic ion sequesterants such as salicylidene diamines are added as a stability-inducing additive to the fuel.
Whether used alone or as part of a fuel stability additive mixture, there is need for corrosion inhibitors adapted for use in oxygenated gasolines that would retain effectiveness over a long period of time.
It has also been found that the carboxylic acid functionality present in certain corrosion inhibitors has a deleterious effect in some additive formulations. While the exact nature of these effects is difficult to determine, it appears that problems arise when the acidic corrosion inhibitor reacts with certain amine bases in additive formulations to form salts which precipitate from solution to form an undesirable sludge. Not only is the instant invention concerned with identifying long acting corrosion inhibitors for oxygenated gasolines, it is desirable to constrain the ratio of acid to amine functionalities in order to minimize undesirable sludge.
Many corrosion inhibitors are known. For example, U.S. Pat. No. 3,663,561 discloses 2-hydrocarbylthio-5-mercapto-1,3,4-thiadiazoles stated to be useful as sulfur scavengers.
U.S. Pat. No. 3,117,091 discloses as rust preventive compounds for a petroleum based carrier such as motor gasoline, aviation gasoline, jet fuel, turbine oils and the like, the partial esters of an alkyl or alkenyl succinic anhydride produced by the reaction of one molar equivalent of a polyhydric alcohol with two molar equivalents of the anhydride.
U.S. Pat. No. 4,128,403 discloses a fuel additive having improved rust-inhibiting properties comprising (1) from 5 to 50 weight percent of a hydrocarbyl amine containing at least 1 hydrocarbyl group having a molecular weight between about 300 and 5000, (2) from 0.1 to 10 weight percent of a C12 to C30 hydrocarbyl succinic acid or anhydride, (3) from 0.1 to 10 weight percent of a demulsifier, and (4) 40 to 90 weight percent of an inert hydrocarbon solvent.
U.S. Pat. No. 4,148,605 discloses novel dicarboxylic ester-acids resulting from the condensation of an alkenylsuccinic anhydride with an aliphatic hydroxy acid having from 2 to about 18 carbon atoms and amine salts of said ester-acid as rust or corrosion inhibitors in organic compositions.
U.S. Pat. No. 4,214,876 discloses improved corrosion inhibitor compositions for hydrocarbon fuels consisting of mixtures of (a) about 75 to 95 weight percent of a polymerized unsaturated aliphatic monocarboxylic acid having about 16 to 18 carbons, and (b) about 5 to 25 weight percent of a monoalkenylsuccinic acid wherein the alkenyl group has 8 to 18 carbons.
U.S. Pat. No. 5,035,720 relates to a corrosion inhibiting composition comprising an oil-soluble adduct of a triazole and a basic nitrogen compound.
U.S. Pat. No. 5,080,686 relates to the use of alkyl or alkenyl succinic acids to inhibit the corrosion of metals in oxygenated fuel systems.
US 2008/0216393 relates to compositions and methods for reducing corrosion and improving durability in engines combusting a fuel containing ethanol and a corrosion inhibitor.
It would be desirable to have long acting corrosion inhibitor or mixtures thereof at low treat rates which would protect fuel distribution infrastructure and internal combustion engines when exposed to a variety of oxygenated fuels, including specifically gasoline blends comprising biologically-derived butanol, under different conditions, and which would not produce high levels of insolubles or cause valve or injector sticking in engines but comprise increased renewable content as compared to other oxygenated gasoline blends.